BCME 1105 Revision PDF

BCME 1105 REVISION Assoc. Prof. Wael Mahmoud ElSayed Shohba 1  What is Entomology (Hexapoda)? Taxonomy: Physical Characters:...

BCME 1105 REVISION Assoc. Prof. Wael Mahmoud ElSayed Shohba 1  What is Entomology (Hexapoda)? Taxonomy: Physical Characters: Exoskeleton Kingdom: Animalia Phylum: Arthropoda 3 pairs of legs Class: Insecta 1 pair of antennae Subclass: Body is divided into 3 regions (Head-Thorax- Abdomen) More than 1 million recorded species Subclass I: Apterygota Subclass II: Pterygota Primitive insects Not-primitive Wingless Wingless or winged Ametabola (No metamorphosis): Incomplete or Complete metamorphosis Eggs>>>>> Young>>>Adult Eggs>>>nymph>>>Adult Eggs>>>larva>>>Pupa>>>Adult 2 Evolution of flight and feeding The insects had experimented with at least two major kinds of adaptation: A- The presence of membranous wings and B- Modifications of mouthparts A- The Presence of membranous wings The Presence of membranous wings is a common characteristic of late Carboniferous fossil insects. The early Carboniferous is so poor, however, we know nothing about the actual evolutionary sequence that led to the winged condition. Paranotal Lobe Theory Prior to the development of functional wings, several fundamental changes in the structure or thoracic segments must have occurred. These changes which involved in the vertical expansion and consolidation of the sclerites that formed the sockets into which legs articulated. This unifunction of of pleural regions of the thorax have enabled the insects to raise themselves and move more quickly. The paranotal lobe theory suggests that the dorsal sclerites of the thoracic segments called “notal plates” expanded laterally to form lobes that extended beyond sides of the body. 3 Some workers threorized that these paranotal lobes served as stabilizers which helped in jumping or falling. Further expansion of these lobes may have produced a set of gliding planes similar to the flaps or skin stretched between the legs of flying squirrels. Such planes would certainly have been useful as means of localized mobility and could have served as an aid to widespread by wind. So that they could be moved up and down over the fulcrum. Paranotal lobe were not beneficial mainly as locomotory stabilizers but were used in enhancement of mate location and selection. 4 B- Posture of the head and the modifications of mouthparts A- Hypognathous: The ancestors of the insects had mouthparts directed downward which is suitable position for feeding. B- Prognathous: The forward direction of the mouthparts was better suited to tunneling or to the active pursuit of prey. Some early fossil insects showed these adaptations as well as some modifications of the generalized form of the mouthparts. C- Opithognathous: Feeding on plant juices by penetration and sucking rather than by chewing. These long styles have been moved out of the way by a background deflection of the front of the head. In the 50 million years after the end of the Carboniferous; the insects diversified greatly. Several new orders come into existence and many of the fossils preserved during that geological period which is known as Permian period. 5  What Is Biodiversity? It can mean the variety of habitats, living communities and ecological processes in an ecosystem. It can mean the diversity of genetic characteristics within a species. It can mean the variety of species in a given area. Why Is Biodiversity Important? Ecosystems depend on the combined contributions of the individual organisms within them. The loss of any species can prevent that ecosystem from operating the way it should. An ecosystem with a high level of biodiversity is more resistant to environmental change. 6 What Is Biodiversity and Why it is important? A species is a set of individuals of the same species that can mate and produce fertile offspring. 8-100 million species total; 2 million species identified (ca. 1.7 million species) The biodiversity found in genes, species, ecosystems, and ecosystem processes is vital to sustaining life on earth.  Keystone species A keystone species is a species that has a disproportionately large effect on its natural environment relative to its abundance. Keystone species play a critical role in maintaining the structure of an ecological community, affecting many other organisms in an ecosystem and helping to determine the types and numbers of various other species in the community. Without keystone species, the ecosystem would be dramatically different or cease to exist altogether. Some keystone species are also Apex Predators. An ecosystem may experience a dramatic shift if a keystone species is removed, even though that species was a small part of the ecosystem by measures of biomass or productivity. It became a popular concept in conservation biology, alongside flagship and umbrella species. Although the concept is valued as a descriptor for particularly strong inter-species interactions, and has allowed easier communication between ecologists and conservation policy-makers, it has been criticized for oversimplifying complex ecological systems. Further, insects are keystone species that provide invaluable ecosystem services that extend beyond pollination, by providing biological control of pests, and acting as bio-indicators of healthy streams and soils. HUMAN is a keystone? 8  Indicator species Indicator species is any species (Bioindicator)) or group of species whose function, population, or status can reveal the qualitative status of the environment. The most common indicator species are animals. For example, copepods and other small water crustaceans that are present in many water bodies can be monitored for changes (biochemical, physiological, or behavioral) that may indicate a problem within their ecosystem. Bioindicators can tell us about the cumulative effects of different pollutants in the ecosystem and about how long a problem may have been present, which physical and chemical testing cannot. A biological monitor or biomonitor is an organism that provides quantitative information on the quality of the environment around it. Therefore, a good biomonitor will indicate the presence of the pollutant and can also be used in an attempt to provide additional information about the amount and intensity of the exposure. A biological indicator is also the name given to a process for assessing the sterility of an environment through. Caddisflies, Mayflies and Chironomids used as an indicator of water quality. 9 Types of Biodiversity Genetic diversity Ecosystem or Ecological diversity Biomes (Desert, Aquatic, Forests, Open lands, etc) Distinct climate Certain species, especially vegetation Functional diversity (Energy flow, matters recycling) Species Diversity Functional Diversity Ecological Diversity The biological and chemical processes such as energy The variety of terrestrial and flow and matter recycling needed for the survival of species, aquatic ecosystems found in communities, and ecosystems. an area or on the earth. Genetic Diversity Species Diversity The variety of genetic material The number and abundance of species within a species or a population. present in different communities  Sometimes landscape (is a heterogeneous land area composed of cluster of interacting ecosystems that is repeated in similar form throughout or mosaic of heterogeneous land forms, vegetation types and land uses) or pattern diversity is considered as broad forum of Ecological biodiversity. Biodiversity: Within the species is genetic diversity Between species is species diversity or taxonomic diversity or organismal diversity At ecological or habitat level is ecosystem or ecological diversity. 12 Changes in Biodiversity, why? Climate change Overhunting Non-native predators and competitors (not subjected to Lotka-Volterra Model) Many species face extinction Pollution (Pb, CO2, CO, SO2, NO2, O3, Particulate matters,…etc)  Ecosystem All Biotic components (living organisms including floral and faunal components) and Abiotic factors (non-living factors including metreological and topographical factors) Species Organisms with similar appearance, anatomy, physiology, biochemistry and genetics that can interbreed freely to produce fertile offspring 14  Speciation One species splits into two or more species that can no longer breed and produce fertile offspring. Or, Groups of population that can actually or potentially exchange genes with one another and that are reproductively isolated from such group. Reproductive barriers Extrinsic barriers Intrinsic barriers Allopatric Allochronic Isolation Sterility Different places Different seasons male/female can Either male not locate each or female are other infertile (Sperm/Ovum) 15  Adapted to cold through heavier Arctic Fox fur, short ears, short legs, and short nose. White fur Northern matches snow population for camouflage. Spreads Different environmental Early fox northward and southward conditions lead to different population and separates selective pressures and evolution into two different species. Gray Fox Adapted to heat through Southern lightweight population fur and long ears, legs, and nose, which give off more heat. 16  Habitat Where individuals of a species live Specific locality, with specific conditions that species may be well adapted to Aquatic habitats Terrestrial habitats Ex. Rivers, streams, lakes, Ex. Deserts, forests, wetlands, water patches, springs forest edges, valleys, agro- ecosystems 17  Ecotope An ecotope is the smallest ecologically distinct landscape features in a landscape mapping and classification system. It is an ecological habitat on the scale of individual organisms sharing space. Many ecotopes together, either adjacent or overlapping, make up a larger unit or eco-region. An ecotope comprises all the constituent parts found at that locality on the same scale, such as the physiotope (landform), the geotope (rocks and soil) and the biotope (living flora and fauna). 18  Ecotone An ecotone is a transition area between two biological communities where two communities meet and integrate. It may be narrow or wide, and it may be local (the zone between a field and forest) or regional (the transition between forest and grassland ecosystems). An ecotone may appear on the ground as a gradual blending of the two communities across a broad area, or it may manifest itself as a sharp boundary line. An ecotone is an area that acts as a boundary or a transition between two ecosystems. A common example could be an area of marshland between a river (aquatic ecosystem) and its riverbank (land ecosystem). Ecotones are of great environmental importance. Because the area is a transition between two ecosystems or biomes, it is natural that it contains a large variety of species of fauna and flora as the area is influenced by both the bordering ecosystems. 19  Ecoline An ecoline is a physical transition zone between two ecosystems. an ecocline is a variation of the physiochemical environment dependent of one or two physico-chemical factors of life, and thus presence/absence of certain species. An ecocline can be a thermocline (temperature gradient), chemocline (chemical gradient), halocline (salinity gradient) or pycnocline (variations in density of water induced by temperature or salinity). An ecotone is often associated with an ecoline. 20 Terminology Individual of a given species (S) >>>>> Individual (Indv.) Individuals making groups >>>>>> Population Set of populations >>>>> Community or Assemblage Set of similar communities >>>>> Biomes Set of communities interacting with the Biotic and Abiotic factors of the environment >>>>> Ecosystem Abundance scales of number of individuals Ecological niches (Habitats) Specific scale used – ‘ACFOR’ Abundant, Generalist species Common, Specialist species Frequent, Occasional, Native species Rare Non-native species 21  Species Diversity Biodiversity is defined and measured as an attribute that has two components: richness and evenness. Richness = The number of groups of genetically or functionally related individuals. In most surveys, richness is expressed as the number of species and is usually called species richness. It is usually symbolized as “S”. Evenness = Proportions of species or functional groups present on a site. The more equal species are in proportion to each other the greater the evenness of the site. A site with low evenness indicates that a few species dominate the site. It is usuallu symbolized as P, which is also equals to P = n/N 22 Types of Biodiversity Biodiversity Can be Expressed at Several Scales (Alpha, Beta and Gamma Biodiversity) Alpha biodiversity is the species diversity present within each ecosystem on a landscape. Beta biodiversity is represented by the species diversity between any two communities. Gamma biodiversity of is the species diversity across the entire landscape, taken as one unit. Scale is absolutely critical in ecological studies. Alpha Diversity = richness and evenness of individuals within a habitat unit. For example in the upcoming figure, Alpha Diversity of sites was as follows: Site A = 7 species, Site B = 5 species, Site C = 7 species. Beta Diversity = expression of diversity between habitats. In the same figure as an example, the greatest Beta Diversity is observed between Site A and C with 10 species that differ between them and only 2 species in common. Gamma Diversity = landscape diversity or diversity of habitats within a landscape or region. In this example, the gamma diversity is 3 habitats with 12 species total diversity. 24 For measuring the diversity of species assemblage, different indices could be applied in order to get more interpretations since each diversity index has a merit over the other. Species diversity (α-diversity) of populations separately considered the number of species in a biocenosis (S), the number of individuals (N), species richness and diversity, and total population uniformity by species. Biodiversity was analyzed by the Shannon’s diversity index (H´), which is sensitive to changes in the abundance of rare species in a community, and by the Simpson’ s index (1-D), which is sensitive to changes in the most abundant species in a community. S = number of observed species N = number of total individuals of all species ni = number of individuals of a specific species pi = evenness, proportion of individuals of a specific species to the total number of all individuals of all species (N), pi = ni / N  Shannon’s diversity index, H´= −Σpilnpi Simpson’s diversity index, (1-D) = Σ {ni (ni – 1) / N (N – 1)} Evenness index = (eH΄/S) where H´ is the Shannon’s index, and S is the number of observed species Species Richness Species richness is the number of different species present in an area. The more species present in a sample the ‘richer’ the area. Species richness is the most commonly used measure of diversity because it is a straightforward measure and it is intuitive. The main problem with using species richness is that it does not provide any information on how well each of the species is represented in the sampled area. There are several simple species richness indices that attempt to compensate for sampling effects by dividing richness, S, the number of species recorded, by N, the total number of individuals in the sample. Two of the best known of these are Margalef’s diversity index and Menhinick’s index. Margalef’s richness index (DMg) Menhinick’s index (DMn)  Indices of similarity Several techniques have been developed to compare communities, based on their species compositions and rank- abundance patterns, across environmental gradients or between areas. The similarity measures allow us to quantify the degree of overlap between the species in the two communities. The similarity measures are a valuable tool because it allows one to determine whether two communities are composed of similar species. The simplest of these similarity measures are indices based on species presence or absence in the communities being compared. The Jaccard’s index (CJ) is calculated as: CJ = j/ (a + b − j) and the Sorenson’s index (CS) as: CS = 2j/ (a + b) where j is the number of species found in both sites, a is the number of species in the first site, and b is the number of species in the second site.  Index of Relative Rarity (IRR) Rare sp. Common sp. 1 100 50 Rarity cut-off point 1- Weight assignation depends upon the chosen rarity cut-off point. 2- IRR is calculated as the sum of the weights of the assemblage’s species, which is divided by the assemblage’s richness, and then normalized between 0 and 1. Occupancy For identifying rare sp: Present-absent Statically Sp-Sp effects and its level covariates relative rarity index (IRR) and ranges 0 – 1, where closer to 1 means more rare species. Rabirowitz identified 3 major axes on which species can be common or rare (With 8 Categories) Local abundance Extent of geographical Habitat specificity (Local population size) area large vs. small wide vs. narrow broad vs. restricted (2 categories) (2 categories) (2 categories) Wide range, broadly adapted, large local population are not rare leaving 7 rarity types  Conservation of biodiversity Conservation is defined as management of human use of biosphere so that it may yield sustainable benefit to the present generation while maintaining its potential to meet the needs and aspirations of posterity. There are two basic strategies of biodiversity conservation In-situ (on site) and Ex-situ (off site).  In-situ Conservation Conservation of organism in its natural home through protection of a group of typical ecosystems by a network of protected areas, biosphere reserves, sacred forests and sacred lakes. Protectorates (Protected Areas) These areas such as National Parks and Wildlife Sanctuaries are areas of land and/or sea especially dedicated to the protection and maintenance of biological diversity, and of natural and associated cultural resources. There are more than 287.359 protectorates all over the world (World Database on Protected Areas WDPA, record of October, 2023). This comprises 275,357 polygons and 12,002 points and covering 244 countries and territories. 32  In Egypt, there are 30 protectorates covering 15% of the terrestrial area, while over 9% of the coastal and near shore environment is protected. Wadi Degla Natural Reserve Ras Mohammed National Park The Petrified Forest protectorate Wadi al-Hitan Saint Catherine  Ex-situ Conservation Conservation of organisms in botanical gardens, zoos, conservation stands, gene, pollen, seed, seedling, tissue culture and DNA banks. There are more than 1500 botanical gardens in the world containing more than 80,000 species and many of these now have seed banks, tissue culture facilities and other ex situ technologies. Similarly there are more than 800 professionally managed zoos around the world with about 3000 species of mammals, birds, reptiles and amphibians. Many of these zoos have well developed captive breeding programmes. Plants and animals conserved in botanical gardens, arboreta, zoos and aquaria can be used to restore degraded land, reintroduce species into wild, and restock depleted populations.  Botanical gardens and Arboreta in Egypt Orman Botanical Garden Aswan Botanical Garden El Nabatat Island  Feeding Habits “Habits” and Trophic levels Trophic level of an organism is the position it occupies in a food web. The trophic level of an organism is the number of steps it is from the start of the chain. In Ecology, we have categorized organisms by the way in which they interact into two categories: Autotrophs Heterotrophs Or Producers 37  Autotrophs These are species that fix the energy comes from the sun and utilize inorganic chemicals to form complex organic molecules. Thus, they are considered as self-nourishing organisms. They produce complex organic matters (such as carbohydrates, fats and proteins) using carbon from simple substance such as Carbon Dioxide (CO2) on which all life depends. They also termed “Producers”. They are generally using energy from light (photosynthesis) or inorganic chemical reactions (chemosynthesis). They convert an abiotic source of energy (e.g. light) into energy stored in organic compounds, which can be used by other organisms A clear example of Autotrophs are green plants on land and algae on water. 38  Heterotrophs These are organisms that cannot produce their own food, instead taking nutrition from other sources of organic carbon, mainly plants or animal matters. In the food chain, heterotrophs are primary, secondary and tertiary consumers, but not producers. Living organisms that are heterotrophic include all animals and fungi and some bacteria. Heterotrophs could be divided into: 1- Consumers: These are organisms that feed on autotrophs and considered “primary consumers”. 2- Saprophagous or Decomposers: These are heterotrophic species that feed on dead organic matters (Plant or animal origin) and play an important role in recycling nutrients in the ecosystem. 39  Consumers Consumers are divided into several groups: Herbivores Carnivores Predators Omnivores Parasites Parasitoids 40  Herbivores They are organisms that feed on plants. A herbivore is an organism that anatomically and physiologically are adapted to feed on plant materials, for example foliage or marine algae, for the main component of its diet. As a result of their plant diet, herbivorous organisms typically have mouthparts adapted for chewing or grinding. 41 Carnivores They are organisms that feed on animals. Carnivorous plants (Insectivorous plants) that feed on insects and other arthropods for extra nutrients such as nitrogen (Protein) Think of insects as vitamin pills for carnivorous plants. Predators They are organisms that hunt, kill and feed on their prey. 42  Omnivores An omnivore is an animal that has the ability to eat and survive on both plant and animal matter. Obtaining energy and nutrients from plant and animal matter, omnivores digest carbohydrates, protein, fat, and fiber, and metabolize the nutrients and energy of the sources absorbed. 43  Parasites A parasite is an organism that lives on or in a “host organism” and gets its food from or at the expense of its host. A parasite lives inside the body of its host is considered and “internal parasite” whereas a parasite lives on the body of its host is considered as an “external parasite”. Parasitism is a close relationship between species, where one organism, the parasite, lives on or inside another organism, the host, causing it some harm, and is adapted structurally to this way of life. 44  Parasitoid A parasitoid is an organism that has young that develop on or within another organism (the host), eventually killing it. Parasitoids have characteristics of both predators and parasites. In general, parasitoids are usually smaller than their selected host. A female wasp laying eggs inside an aphid using long ovipositor 45  Different types of parasitoidism Hyperparasitoid Superparasitoid Multiparasitoid (Metaparasite) Superparasitism is a form in which A hyperparasite, also known as a the host is attacked more than once metaparasite, is a parasite whose host, by a single species of parasitoid. often an insect, is also a parasite, often specifically a parasitoid. Multiparasitism or “coinfection” occurs when the host has been parasitized by more than one species. 46  Food Chain It is an interlocking linear feeding links among different organisms starting from producer organisms (green plants or algae which produce their own food via photosynthesis) and ending at an apex predator species. The length of a food chain is a continuous variable providing a measure of the passage of energy and an index of ecological structure that increases through the linkages from the lowest to the highest trophic (feeding) levels. 47  Food Web A variety of interactions results in a complex mesh of relationships. A food web is the natural interconnection of food chains and a graphical representation of “what-eats-what” in an ecological community. Another name for food web is “consumer-resource system”. 48  Ecological Pyramids Ecological pyramid is also known as Trophic pyramid, Eltonian pyramid, or Food pyramid. It is the graphic representation of an ecological parameter (like the number of individuals, biomass or energy) present in various trophic levels of a food chain with producers forming the base and carnivores the top. Pyramid of Number Pyramid of Biomass Pyramid of Energy Pyramids of biomass and energy are harder to prepare but they are more accurate and not inverted. This is because energy always lost between trophic levels leading to reduce biomass and this maintains the pyramid shape. 49 Pyramid of Number Compares the number of organisms at each trophic level. It is the easiest to prepare and easier in calculating the energy or biomass, however, it is misleading and inverted. 50  Pyramid of Energy Compares the amount of energy passing through each trophic level over a period of time. Pyramid of Biomass Compares the mass of biological material at each trophic level. 51 Insect sociobiology  Locust swarm What is the different between insect societies and insect swarms? Mosquito swarm Monarch Butterflies swarm  Swarm or swarming, is a collective behavior exhibited by entities, particularly animals, of similar size which aggregate together, perhaps milling about the same spot or perhaps moving in masses or migrating in some direction. As a term, swarming is applied particularly to insects, but can also be applied to any other entity or animal that exhibits swarm behavior. Characteristics of insect societies They live in groups of closely related individuals Individuals are usually faithful to their “family” Often live in a confined locality (“nest, hive”) In eusocial insects Overlapping generations: parents live with offspring Members collaborate in raising the offspring Sterility of a large number of individuals of the colony (e.g. “workers”, “soldiers”): reproductive division of labour  Degrees of sociality Solitary (none of the features on previous slide) Subsocial: the adults care for their own young for some period of time (e.g. cockroaches) Communal: insects use the same composite nest without cooperation in brood care (digger bees) Quasisocial: use the same nest and also show cooperative brood care (Euglossine bees) Semisocial: in addition to the features in quasisocial, also has a worker caste (Halictid bees) Eusocial: in addition to the features of semisocial, there is overlap in generations (Honey bees): offspring assist parents  In honeybees, one queen and up to 40,000 workers In bumblebees, one queen and 20-500 workers  Size of insect societies In wasps, 1 to 1000s of queens and 1000s to millions of workers In ants, 1 to over a million queens; up to many million workers  One Japanese red wood ant colony contains 307 million ants, including some 306 million workers and about 1.1 million queens. In Hymenoptera, the workers are invariably female; the males are only for mating. Termites also have male workers  They were the first animals which started living in colonies and developed a well organized social system about 300 million years ago, much earlier than honey bees and ants. Although termites do not exceed 3-4 mm in size, their queen is a 4 inch long giant that lies in the royal chamber motionless since its legs are too small to move its enormous body. This phenomenon of enormous enlargement of abdomen in termite queen is called physogastry. Termite queen is an egg-laying machine that reproduces at the astonishing rate of one egg per second, 24 hours a day and for about 20 years of life. Producing eggs is the only mission in the life of a termite queen The other castes, workers and soldiers are highly devoted to the colony, working incessantly and tirelessly, demanding nothing in return from the society. Workers have to take care of all its daily chores. workers chew the wood to feed to the queen and larvae and grow fungus gardens for lean periods. Soldiers have long dagger-like mandibles with which they defend their nest. Nasutes are specialized soldiers which specialize in chemical warfare. They produce a jet of highly corrosive chemical from their bodies that can dissolve the skin of enemies and can also help in making galleries through the rocks. They are bulldozers of the colony. Unlike honey bees, termite adults are diploid in both sexes as they develop from fertilized eggs. Queen secretes inhibiting hormones that do not allow nymphs to develop into new queens. Differentiation of different castes in termites takes place by feeding the larvae with saliva of workers. Larvae that are fed on more saliva develop into sexual forms while nymphs that are fed on wood and fungus develop into workers and soldiers. Worker Termite Nasute Termite Soldier Termite  Reproduction There is of course a complex interplay of physical and biological factors that determine how quickly increase in number. The sequence of events must begin with reproduction and the development of individuals with the capacity to give offspring. The reproductive process consists of the following sequences of events: Mate location: mechanisms and behavior Copulation: Coupling of male and Ejaculation: Release of sperm by male that bring potential mates together female genital apparatus Insemination: Introduction of sperms into female reproductive system Courtship: Behavior patterns lead to pairing of male and female Fertilization: Penetration of an egg by sperm and uniting of nuclei Embryogenesis: Early stages of development within the egg Oviposition: Deposition of fertilized egg by the female Eclosion: Hatching of eggs and release or escape as larval insect 61  Modes of Reproduction Ovoviviparity Oviparity The eggs are retained within the body of the female until The eggs are laid following various degrees of they hatch and then the young individuals are released. embryonic development but they do not hatch Ovoviviparity has the advantage of reducing the time that until sometimes after oviposition and the the egg stage is exposed and the environmental conditions conditions are favorable for survival: must be suitable for the survival of young progeny as they Eggs may hatch within 2 days and others may are normally less tolerant of adverse conditions than the not hatch within for 2 years. eggs. The fully developed eggs hatch immediately after The longer the defenseless eggs are exposed, being laid or just prior to ejection from the female’s the more subject they are to mortality factors. reproductive tract. Egg pouch Solitary eggs 62  Viviparity The young are nourished for some period within the body of the female and released in a more advanced state of development than in ovovivipaity. Ex: Cockroaches, earwigs and bugs. Milk gland The uterine or milk glands in tsetse The eggs are deficient in yolk and the embryos are nourished flies (Glossina sp.) are modified female in a brood pouch by a close maternal tissue called accessory reproductive glands which “Pseudoplacenta” and the tissues of embryo. In one group of elaborate and release a nutritive liquid of flies (Cecidomiidae), the larvae develop in the mother’s body proteinaceous and lipoid nature for the by feeding on her tissues. maturing intrauterine larva In other dipterans, the larvae are nourished by the female and grow to full size in her vagina. They become pupae after they are deposited. In such case of reproduction, no external source of larval food is necessary. 63  Paedogensis Reproduction by the juveniles. This is an unusual form of parthenogenesis, occurring chiefly in the gall midges (Cecidomyidae), in which the larvae or rarely the pupae give birth to living young. Other insects speed up reproduction by depositing their young in an advanced stage of development. This occurs chiefly in the parasitic Diptera. The fully grown larva or puparia are deposited by adults of these species. Paedogenesis is usually associated with both the parthenogenesis and viviparity. This phenomenon occurs apparently as a result of hormone imbalance and is often associated with generation cycles. This strange means of reproduction seems to be rather good way to exploit favourable food conditions without wasting energy on the development of winged adults, unless needed. 64  Parthenogenesis Parthenogenesis is a form of asexual reproduction whereby offspring are produced without the embryo being fertilized by a male. There are a reasonable number of species of insect that can reproduce parthenogenetically but perhaps the most well know is the Aphids and Bees. In this species, like most other parthenogenetic species, the females lay unfertilised eggs which hatch into females which also lay unfertilised eggs and so on. Parthenogenesis can be: Accidental: occasionally, an unfertilized egg gives birth to a larva; ex Bombyx mori (silkworm butterfly). Facultative: while some eggs are fertilized, others not. Obligated: eggs only develop if they are unfertilized. It occurs in many species. Moreover, depending on the chromosomic number of the ovule, parthenogenesis can be: Arrhenotoky [Haploid (n)] and Thelytoky [Diploid (2n)]: unfertilized eggs (n) generate males and fertilized eggs (2n), females. It takes place in bees and it is always facultative. Sex determination at birth is a key process in the evolutive history of colonial structures in social insects. A- Parthenogenesis in bees In honeybees, fertilized eggs give birth to females (workers or queen depending on the diet they are given during the larval stages) and unfertilized eggs, to males. 65 66 Difference between Arrenotoky and Thelytoky 67  B- Parthenogenesis in Aphids Overwintering egg, diploid for both types of chromosomes (AA and XX) gives birth to an asexual female. After several cycles of parthenogenesis, asexual females produce sexual females and males. Males inherit the same autosomal genome as asexual females, but receive only one of the female Xs: hence they are diploid for the autosomes and haploid for the X (represented as AAX0). Ovules (haploid for both the autosomes and the X) are generated by a normal meiosis, but males produce only X- bearing sperm (AX). The fusion of male and female gametes restores the diploid level at both the X and the autosomes. 68 Thank you Good Luck